Virtually all commercial bakery ovens utilize combustible gas and electrically operated controls for enabling and disabling the flow of gas to each oven. It is fairly common for electrical energy interruptions and reductions, referred to as brownouts, to occur. Virtually all commercial baking ovens include controls responsive to energy interruptions and brownouts for instantly disabling the supply of fuel to each oven, thereby avoiding the delivery to and accumulation of unburned combustible fuel in a hot oven.
Following termination of the flow of fuel to the oven, virtually all of the commercial oven installations require the performance of a relighting procedure which involves, in most cases, purging of the oven, opening dampers and doors, starting fans and blowers, acknowledging alarms, cycling switches, and waiting for the purge to be completed before the oven can be relighted. Should the energy failure or brownout occur during a baking cycle, the baking is terminated until such time as the oven can be relighted.
The relighting process often requires a significant period of time, such as twenty minutes or more. The product that is in the oven when the baking cycle is interrupted thus becomes burned or under-baked and is known as a cripple. If the cripple can be sold at all, it is sold at a price considerably under that at which a first quality product is sold. Often, however, the entire content of an oven must be scrapped. The cost of a power failure or reduction, therefore, even for an extremely short period of time, can lead to a loss in excess of several thousand dollars.
The problems associated with the temporary shutdown and relighting of an oven are well known and many attempts over the years have been made to solve them. For example, it has been proposed to utilize stand-by generators with associated power monitoring and transfer equipment, but this proposal has not met with a great deal of success, primarily because it is not possible to transfer power rapidly enough from the principal source to the stand-by source to maintain the oven in operation. Another reason this proposal has not been used widely is the relatively high expense involved in connection with the stand-by equipment.
It also has been proposed to use capacitor banks to keep the main gas supply valves open for a few seconds following power failure or reduction, but during this time gas continues to flow into the oven without being burned. This proposal also has not been widely accepted because management of many bakeries considers the discharging of unburned gas into a hot oven to create an unsafe condition.